An income shares formula is used by many states to establish the child support amount of each child rather than what it actually costs to raise a child. income shares tables calculating child support are not based directly on actual spending on children but rather on indirect estimates of child costs. income shares assumes that child costs reflect the spending necessary to restore a family's standard of living back to what it was prior to the divorce or having a child. This technique was first developed in the 19th century to answer economic questions among different family types, but was never intended to measure the cost of rearing children.

Approximately half of all guidelines for child support in the United States are based on the income shares child support model. The income shares model for child support was developed by economist Dr. Robert G. Williams and was based on the work of Thomas Espenshade. Espenshade analyzed the 1972–1973 Consumer Expenditure Survey to determine the costs of raising children in the United States. The number of states using the income shares model is decreasing.